Alkylation refers generally to the addition of an alkyl group to an organic compound. One well-known alkylating agent useful in the preparation of a wide variety of alkylated derivatives is the olefin. For example, "isooctane," a high octane number petroleum fraction, which is valuable as a fuel may be prepared by the alkylation of isobutane and 2-butene. Other similarly highly branched hydrocarbons may be prepared in an analogous manner by varying the olefin and the isobutane reactants. This specific alkylation process may be carried out thermally or in the presence of an acid catalyst, such as hydrogen fluoride or sulfuric acid. The thermal alkylation process is not generally used because of the high temperatures required and the undesired distribution of products resulting from the thermal alkylation.
The acid catalyzed alkylation process is subject to various difficulties also, one very important one being recovery of the spent acid from the alkylated product.
In the acid catalyzed alkylation process, the ratio of isobutane to olefin must be maintained at a high level and the heat of reaction quickly dissipated to minimize the formation of olefin polymers and/or alkylated products comprising more than one added olefin unit.
Alkylation processes are also used to prepare various useful alkylated derivatives of benzene and naphthalene. For example, dodecylbenzene, a useful precursor for the surfactant industry may be prepared by the alkylation of benzene with dodecene in the presence of an aluminum chloride catalyst. The aluminum chloride catalyst continuously deactivates and forms a sludge which is recovered and regenerated only at great cost and difficulty. In all of these processes a solid catalyst which is easily separated from the reaction mixture is desirable.
Other examples of commercially important alkylation processes include the alkylation of benzene with ethylene or propylene to yield ethylbenzene, which may be subsequently converted to styrene; and cumene, which may be subsequently converted to phenol and acetone, respectively. Catalysts useful in these processes include phosphoric acid supported on kieselguhr and aluminum chloride. In each of the above benzene alkylation processes the tendency to form polyalkylated derivatives, as impurities, is a noted problem.
In U.S. Pat. Nos. 3,037,052; 3,017,441; and 3,239,575, the use of various forms of sulfonated polystyrene as a catalyst for alkylation processes is disclosed. The difficulties of using sulfonated polystyrene include (1) cleaning residual organic "tars" from the catalyst; (2) gradual changes in the catalyst properties due to the alkylation of unsulfonated styrene residues; and (3) physical fragility of highly sulfonated styrene-divinyl benzene copolymers. In all of these patents, there is no mention of the use of polyfluorosulfonic acid polymers as catalysts for the alkylation processes described therein.